1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to transmitting and receiving radio frequency (RF) signals, and more particularly to an RF receiver and an RF receiving method which processes a baseband signal in which a direct current (DC) offset is removed in a demodulator.
2. Description of Related Art
A transceiver that transmits and receives a radio frequency (RF) signal is utilized in a system for transmitting/receiving high speed wireless data, such as a mobile phone, a digital multimedia broadcasting (DMB) phone, and a personal digital assistant (PDA). A transmitter transmits data by including the data in a predetermined carrier signal. A receiver extracts data by processing a received RF signal. Presently, the development of a transceiver, which can be miniaturized with low power consumption even in a ubiquitous system of a multi-band orthogonal frequency division multiplexing ultra-wide band standard (MB-OFDM UWB), is an important issue in the design and implementation of various types of portable systems.
FIG. 1 is a diagram illustrating a conventional RF receiver 100. Referring to FIG. 1, the RF receiver 100 includes an in-phase mixer (I-mixer) 110, a quadrature-phase mixer (Q-mixer) 130, low pass filters (LPFs) 120 and 140, and a demodulator 150.
The I-mixer 110 multiplies and frequency-down converts a received RF signal RXIN and a local oscillator signal LOI. In this instance, a signal obtained by the multiplication is processed in the LPF 120 and an output of the LPF 120 is input into the demodulator 150. The Q-mixer 130 multiplies and frequency-down converts the RF signal RXIN and a Q signal, LOQ, of the local oscillation signal LOI. In this instance, the signal obtained by the multiplication is processed in the LPF 140 and an output of the LPF 140 is input into the demodulator 150. The demodulator 150 demodulates the outputs of the LPFs 120 and 140 according to algorithms, such as phase shift keying (PSK), quadrature phase shift keying (QPSK) and amplitude shift keying (ASK), and obtains certain information contained in the signal that is demodulated. The demodulated signal may be further processed in a post processor. Also, the demodulated signal is indicated as information that a user can recognize, via an audio output device or display, such as a mobile phone, a DMB phone, a PDA, and a radio frequency identification (RFID) reader.
As described above, circuits for separately processing an I-path and a Q-path in preparation for a noise component received with the RF signal RXIN are added in the conventional RF receiver 100. Accordingly, circuits become more complicated and power consumption increases. Also, a direct current (DC) offset may be present in an output of the mixers 110 and 130 due to the received noise component. Accordingly, a circuit for removing an effect of the DC offset has to be added in the demodulator 150. Also, the received noise component described above may be introduced from a directional coupler (DCPLR) which is utilized in a transceiver of a general full-duplex communication method. As an example, a transceiver of a system such as an RFID tag reader transmits/receives an RF signal via one antenna. In this case, a leakage of a transmitting RF signal may be introduced into a received RF signal from a DCPLR connecting transmitting and receiving paths.